Conventionally, the upstream end of a turbine engine comprises a fan comprising a wheel formed of a plurality of blades surrounded on the outside by an annular casing which can made of a metal material or of a composite material comprising a matrix integrating reinforcing fibres, such as a polymer matrix, for example, epoxide polymer, and carbon fibre or glass fibre reinforcing fibres. This casing enables an initial compression of air entering in the turbine engine and also ensures a function for confining the blades in case of loss of one of them. The fan casing is surrounded by a plurality of equipment supply ducts, in particular, by a pressurised air supply duct, at a temperature of around 200° C., an engine called APU (auxiliary power unit) used to start the turbojet as well as supplying the aircraft cabin with electricity when the aircraft is grounded.
In case of malfunctioning, such as a leak from the pressurised air supply duct, the air can lead to a significant local heating of the casing, since the temperature of the air is around 200° C. When the casing is made of a metal material, for example, aluminium, the heating is not impacted by the mechanical integrity of the casing. In the case of a matrix fan case integrating the reinforcing fibres, the mechanical strength thereof following being heated, must be able to be guaranteed.
Therefore, it is understood that the non-destructive test of a composite matrix casing with reinforcing fibres is particularly important, and all the more so, as a composite casing is proving to be very expensive.
It has thus been proposed to apply thermosensitive paints on the casing. However, the lifespan of these paints highly limits their interest, since an engine can be used for period longer than the lifespan of these paints, in particular for long- or medium-haul aircraft. Furthermore, during the placing of an engine, this conventionally undergoes cleaning by scraping, which causes a total removal of the layer of thermosensitive paint, involving another step of applying a layer of paint. Finally, if a thermosensitive paint enables to visually consider the heating state of a given zone of a fan case, it only proves to be an indirect measurement of the state of the internal structure of the casing and does not enable a specific quantification of the internal structure of the casing.